This invention generally relates to the art of electrical connectors and, particularly, to a method and structure for controlling the impedance in electrical connectors by controlling the impedance of the terminals of the connectors.
In high speed electronic equipment, it is desirable that all components of an interconnection path be optimized for signal transmission characteristics, otherwise the integrity of the system will be impaired or degraded. Such characteristics include risetime degradation or system bandwidth, crosstalk, impedance control and propagation delay. Ideally, an electrical connector would have little or no effect on these characteristics of the interconnection system. In other words, the system would function as if circuitry ran through the interconnection without any effect on the system. However, such an ideal connector is impractical or impossible, and continuous efforts are made to develop electrical connectors which have as little effect on the system as possible.
Impedance and inductance control are concerns in designing an ideal connector. This is particularly true in electrical connectors for high speed electronic equipment, i.e., involving high frequencies. An example of one such connector is a board-mounted connector adapted for mounting on a printed circuit board and for mating with a complementary second connector. The connector includes a dielectric housing in which a plurality of terminals are mounted. Each terminal includes a contact portion, such as a contact blade, and a terminating portion, such as a terminal tail.
One exemplary obstacle to providing a consistent impedance across an electrical connection occurs when contact portions of terminals are mounted in a spaced-apart relationship in the dielectric housing of an electrical connector. The contact portions of terminals typically have a broad plate area relative to the rest of the terminal to assure adequate and reliable contact. The contact portions which are separated by a dielectric increase the capacitance of the terminals at the contact portions. Because impedance is inversely related to capacitance, the increase in capacitance causes an impedance drop in the terminals, thereby greatly disrupting the characteristic impedance through the overall electrical system.
This phenomena is illustrated in FIG. 22 in which impedance (Z) is plotted over distance along a terminal in a connector to provide an impedance curve for a conventional terminal. Zo is the average or characteristic impedance of the terminal over the distance of the terminal. The dip at Zmin is the lowest impedance exhibited over the terminal at the contact portion. The greater the capacitance increase at the contact portion, the greater the impedance drop with respect to the characteristic impedance Zo and the greater the connector affects the electrical performance of the electrical system. Conversely, the peak at Zmax represents the increased impedance of the tail portion at the end of the terminal which has a smaller plate area relative to the contact portion.
The invention is directed to a method and structure for tuning the impedance of an electrical connector, such as the connector described above, so as to adjust the impedance of the terminal and/or to minimize the range of deviation from the characteristic impedance of the system. The invention is specifically directed to tuning the connector by trimming or removing a section of the terminals of the connector.
An object, therefore, of the invention is to provide a new and improved method and structure for tuning the impedance of an electrical connector by selectively trimming a section of the terminals of the connector.
In the exemplary embodiment of the invention, generally, the connector includes a dielectric housing having a plurality of terminals mounted in the housing. Each terminal includes a contact portion at one end thereof and a terminating portion at an opposite end thereof. Each terminal has a contact area for mating to a respective terminal of a complementary connector to comprise a mated terminal pair.
The invention contemplates a method and structure in which a desired impedance is determined for each terminal in the connector. The contact area of the contact portion of each terminal is determined. The contact portion, except for the contact area thereof, is selectively trimmed to a given size to reduce the plate area of the contact portion according to the determination of the desired impedance of the terminals. By reducing the plate area of the contact portion, the capacitance at the contact portion of the terminal is reduced to increase the impedance Zmin at the contact portion, thereby increasing the characteristic or average impedance Zo of the terminal. This procedure also has the result of diminishing the range of deviation of the impedance from the characteristic or average impedance Zo for the terminal. By increasing Zmin , Zo is increased and brought closer to Zmax which is determined by the terminal tail.
As disclosed herein, the contact area of the contact portion of each terminal is generally centrally located between side edges of the contact portion. All or part of the side edges may be trimmed to adjust the impedance or, alternatively, apertures or recesses may be formed in the contact portion on opposite sides of the contact area. Still further, the contact portion defines a front end of the terminal, and the front end may be trimmed to vary the impedance. Furthermore, a rear section of the contact portion may also be trimmed to vary the impedance. Preferably, the terminals are formed by stamping the terminals from sheet metal material, and the contact portions can be trimmed during the stamping operation.
The invention also contemplates selectively trimming the tail portion of the terminal to adjust the plate area of the tail portion. By reducing the plate area of the tail portion, the capacitance is decreased and the impedance Zmax of the terminal at the tail portion is increased, and the deviation of the impedance at the contacting interface area is increased thereby increasing the characteristic impedance Zo. By increasing the impedance Zmax at the tail portion, relative to the characteristic impedance Zo and Zmin, the range of deviation between Zmax and Zmin is expanded.
This invention also contemplates adding plate area to the tail portion to adjust the impedance. By enlarging the plate area of the tail portion, the capacitance of the tail portion is increased and impedance Zmax at the tail portion is decreased to decrease the characteristic impedance Zo. By reducing the impedance Zmax at the tail portion relative to Zo and Zmin, the range of deviation between Zmax and Zmin is contracted along the length of the terminal.
Another embodiment of the invention contemplates a terminal having a drive shoulder between the contact portion and the terminating portion of the terminal, to facilitate inserting the terminal into its respective terminal-receiving passage in the connector housing. The drive shoulder is selectively located at a given position longitudinally of the terminal to vary the relative plate areas of the contact portion and the terminating portion as necessary to achieve a desired impedance in the terminal and/or minimize the deviation of the impedance from the characteristic impedance of the electrical system.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.